The present invention relates to the field of power systems, and more particularly to an algorithm for rapidly reducing power to ports in the event of a failure of one of a plurality of power sources.
The growth of local and wide area networks based on Ethernet technology has been an important driver for cabling offices and homes with structured cabling systems having multiple twisted wire pairs. The ubiquitous local area network, and the equipment which operates thereon, has led to a situation where there is often a need to attach a network operated device for which power is to be advantageously supplied by the network over the network wiring. Supplying power over the network wiring has many advantages including, but not limited to; reduced cost of installation; centralized power and power back-up; and centralized security and management.
Several patents addressed to this issue exist including: U.S. Pat. No. 6,473,608 issued to Lehr et al., whose contents are incorporated herein by reference and U.S. Pat. No. 6,643,566 issued to Lehr et al., whose contents are incorporated herein by reference. Furthermore a standard addressed to the issue of powering remote devices over an Ethernet based network has been published as IEEE 802.3af-2003, whose contents are incorporated herein by reference.
Power over Ethernet is typically a scalable technology, in which an initial installation may supply power functionality to a limited number of ports in the system. Over time, additional ports may be powered, with a resultant need for additional sources of power. Each port supplies power to a connected powered device, with power being transmitted from the port to the powered device over the structured communication cabling. One well developed method of adding additional power to a system is the use of a plurality of power sources, or power banks, which are connected together in a “wired or” type arrangement. Other methods of connecting power systems in parallel are known to those skilled in the art, and include any method which is operable to supply the sum of the connected power sources to one or more connected loads.
A major difficulty in the use of a plurality of power sources is the action that must be taken in the event of a failure, or reduced output, of one of the plurality of power sources. For example, in a network in which power over Ethernet is supplied, powered devices receive their power from a central power sourcing equipment. In the event of a failure of one of the plurality of power sources powering the central power sourcing equipment, some ports of the power sourcing equipment supplying power to some powered devices must be disabled so as to avoid an excess load on the remaining power sources. Furthermore, the powered devices which are not to be disabled are preferably to be shielded from any adverse effect from the failed power source. This requires rapid action in the case of power source failure, preferably by disabling sufficient ports so as to reduce the total power drawn by the connected powered device within a short time period, such as 20 milliseconds, or more preferably 2 milliseconds. Disabling sufficient ports prevents an overload condition on the remaining power sources. It is to be understood that shutting down power to a port is herein used interchangeably with disabling a powered device, since each powered device is connected to a specific port.
In prior art systems, in the event of a failure of one or more power sources, ports supplying power to powered devices are individually turned off, and the resultant overall power consumption, or overall current draw, is monitored. Once power consumption has been reduced to a level lower than the power available, the prior art algorithm ceases. Such an algorithm eventually succeeds in balancing the power consumption with the reduced available supply; however the algorithm is slow and requires multiple actual power consumption measurements. Unfortunately, during operation of the prior art algorithm, a mismatch exists between power consumption and power availability, which leads to either overheating of the remaining power sources, or a dip in the power being supplied to those powered devices that have not been disabled. Such a dip in power, which may be manifested as a reduced voltage, can negatively affect the performance of those powered devices resulting in unintended failures.
What is therefore needed, and not known in the prior art, is a method for rapidly identifying and disabling ports in the event that power consumption exceeds available power. Preferably, such an algorithm allows for stabilizing power in the event of a failure indication of one or more connected power sources in less than 20 milliseconds, even more preferably less than 2 milliseconds.